Figure 6.

Comparison of N15 Cro (A) and λ Cro (B) (PDB ID 6CRO) dimers, with the two chains colored differently in each case. For N15 Cro, close contacts between helix 4 from each subunit are illustrated by showing interactions between Ser 42 and Val 46. For λ Cro, ionic interactions among Glu 54 and Lys 56 are shown, as is Phe 58, which extends from the end of strand 3 in one monomer into the hydrophobic core of the other, forming a “ball-and-socket.” Note the similar orientation but different spacing of the two recognition helices in each dimer, which are the helices nearest the viewer in this perspective, indicated by arrows. This figure was prepared using PyMOL (DeLano Scientific).